In Situ Monitoring of the Impact of Liquid−Liquid Phase Separation on Drug Crystallization by Seeding

Abstract

the impact of a liquid-liquid-phase separation (LLPS) or demixing on solution crystallization in quiescent medium of a pharmaceutical compound, C 35 H 41 Cl 2 N 3 O 2 , in an ethanol/water mixture was presented. In this contribution, drug crystallization experiments by seeding are monitored by in situ turbidity, focused beam reflectance measurement, and video microscopy. Two cases are studied: in the first case for seeding experiments in the metastable zone for nucleation and outside the demixion zone we observe the classical secondary nucleation and growth mechanism. In the second case for seeding experiments in the demixion zone, the first stage is the growth of crystals as well as the growth and coalescence of droplets; in the second stage crystals and droplets are still growing and droplet heterogeneous nucleation occurs; and in the last stage, droplets disappear and the secondary nucleation starts. LLPS changes the medium and the conditions of crystallization, prevents the drug nucleation, both primary and secondary, and consequently affects the process. Depending on the point of seeding in the phase diagram, inside or outside the LLPS region, the crystallization mechanisms and kinetics are different.

Exploring Bovine Pancreatic Trypsin Inhibitor Phase Transitions

“…In the cases of lysozyme and BPTI, the metastable liquid phase impedes the nucleation of the solid phase, which was also observed for some organic molecules. 44,45 Note that recently, in an extremely interesting paper from Vivarès et al 46 on the crystallization of glucose isomerase in the presence of a metastable LLPS observed by confocal scanning fluorescence microscopy, it has been shown that nucleation and crystal growth mainly occurred inside the dense phase. Finally, we propose the following practical rule for crystallization: when we observe a demixion, it is bound to be metastable with respect to crystallization and therefore the best crystallization temperature is T, with T e > T g T L-L , where T e is the crystal-liquid equilibrium temperature.…”

Phase equilibrium and mechanisms of crystallization in liquid–liquid phase separating system

“…Liquid-liquid equilibrium data have been investigated for some "anti-solvent" crystallization experiments [2,3], spherical crystallizations using a three solvents system [4,5], oiling out phenomena [6][7][8][9][10] and reverse addition processes [11]. The LLPS makes crystallization difficult in protein systems [12,13], prevents drug nucleation [14][15][16], and hinders nucleation in crystallization of droplets [17]. Lack of phase diagram data for crystallization processes with LLPS makes it difficult to understand, design and control the process.…”

Experimental investigation and prediction of oiling out during crystallization process

“…Oiling out has firstly been detected for solutions of large molecules like proteins and polymers [1][2][3][4][5][6][7] due to the different molecular sizes of polymer and solvent. Recently, experimental studies proved the existence of oiling out also for mixtures containing organic substances with low molecular weights [8][9][10][11][12][13]. However, none of the literature references reported the feasibility of modeling or even predicting the oiling-out behavior.…”